👷 Don't install difficult MILP solver deps

Author: adamsardar

.github/workflows/R-CMD-check.yaml

@@ -41,7 +41,10 @@ jobs:
 
       - uses: r-lib/actions/setup-r-dependencies@v2
         with:
-          extra-packages: any::rcmdcheck
+          extra-packages: 
+            any::rcmdcheck
+            testhat
+          dependencies: '"hard"'
           needs: check
 
       - uses: r-lib/actions/check-r-package@v2